In certain industries, such as the petroleum industry, partial stroke testing of emergency shutdown valves (ESVs) is increasingly required by regulatory bodies. However, ESVs and/or other valve assemblies that are part of “Safety Instrumented Systems” (SISs) are generally designed for on/off operation and connections between valve stems and actuators are not tight, resulting in significant lost motion. Further, ESVs are typically characterized by high seal friction and prominent stick-slip dynamics. All of these factors contribute to poor throttling control and complicate partial stoke testing.
In addition, ESVs and/or other components of SISs are typically high gain devices. For example, SIS actuators are often single action pistons with a spring return. A very small change in pressure within a chamber of an actuator can cause a large movement of the piston. As a result, when coupling SIS actuators, or other SIS components, to process control devices (e.g., to perform partial stroke tests or other tests), biases of the process control devices, such as I/P (current to pressure) biases, can have a dramatic impact on the calibration of the SIS components. If a calibration of the SIS components is off by a significant amount, results from tests on the SIS components, such as partial stroke tests, will be meaningless.